New York, New York -
(NBC News) One of the most expansive mammography studies to date is casting new doubt about the value of the screening intended to detect breast cancer.
It found regular mammograms did not reduce death rates, bucking medical guidelines that women over 40 get screened annually.
Canadian researchers profiled nearly 90,000 women over 25 years and found the screening didn't saves lives, and nearly a quarter of the time led to false alarms.
Still, some doctors are calling the study "flawed" and the American Cancer Society is adamant screening saves lives and women should keep it up.
"This is one page in a very large book on breast cancer screening so I don't think this one study should be a game changer in any way," says Dr. Otis Brawley.